Wood is a naturally occurring composite material being made of wood fibers embedded in a matrix of lignin. Thus lumber made from harvested wood has strength properties which are dependent on the orientation of the fibers or wood grain. Recently the convergence of two trends in the development of wood products has led to the development of new engineered wood-based structural members. The first trend is the increasing costs of wood due to increased demand and decreased supply due to environmental restrictions on logging. In the past, wood unsuitable for forming dimensional timber was often discarded or burnt as waste fuel. Now, however, scrap wood is reduced to wood chips for use in papermaking, particle board or engineered structural members. The second trend is the result of an insight from the structural composites industry marking the realization that composite materials may be engineered to suit particular applications. The result has been products such as wafer board or chip board which have randomly oriented chips or wafers of wood which are laminated together to form a plywood replacement product which is not only cheaper but stronger than plywood in many applications.
Structural timbers are composed of wood chips in which the chip fibers are oriented in the direction of the principle stresses. The wood chips are laminated under heat and pressure to form large laminated loaves which are in turn milled into structural members. The process allows the fabrication of wood structural members which do not require large or uniform logs as starting materials. Further, because the structural properties of the member may be designed, the beam may be stronger and lighter than one constructed of wood boards.
The wood chips or wafers utilized in the construction of these new wood products are fabricated from a wide range of raw logs and wood scraps. Typically the wafers are forty to sixty thousandths of an inch thick, four to twelve inches long, and one-half to three inches wide. In the production of strand board in particular, and structurally engineered wood products in general, it is desirable that the strands not be too wide. This allows better control of the orientation of the strands to achieve the structural properties desired, particularly the random orientation of the strand layers in strand board.
Wafers of uniform width also improve the overall appearance of the product by yielding a uniform surface and by facilitating improved uniformity of the glue coating on the wafers. Slicing the wafers into wafers of proper width presents several problems. The wafers must be precisely oriented as they are fed into the knives to prevent the knives from cutting across the grain and so cutting the fibers in the wafers. It is also desireable to minimize the fines produced by cutting the wafers, as small particles are unacceptable for use in the formation of wafer board.
What is needed is a process and apparatus for splitting strand boards into narrow, uniform lengths without the destruction of useful fiber.